package main

func main()  {
	var aaa []int
	aaa = append(aaa,[]int{}...)
}

type houxuTreeNode struct {
	val int
	left *houxuTreeNode
	right *houxuTreeNode
}

func getHouxuArr(root *houxuTreeNode) []int {

	var ret []int
	if root == nil {
		return []int{}
	}

	ret = append(ret,getHouxuArr(root.left)...)
	ret = append(ret,getHouxuArr(root.right)...)
	ret = append(ret,root.val)
	return ret
}